In conventional practice, pipe laying comprises the steps of excavating a trench and reinforcing the structural integrity of the trench by fitting a trench box therein. The floor of the trench may then be leveled with aggregate, for example gravel, or other suitable material. A pipe is subsequently lowered into the trench, whereupon labourers disposed within the trench manipulate the lowered pipe so as to engage the pipe with previously laid pipe sections. The remainder of the trench is infilled to completely cover the laid pipe.
Principal amongst the difficulties associated with the traditional pipe laying techniques is that trench work is extremely hazardous. The threat of injury or death to workers resulting from trench cave-ins is a recurrent possibility. Moreover, the costs associated with enacting protective measures to prevent workers in the trenches from being trapped or seriously injured in the event of trench wall collapse are considerable.
A summary of current best practice for the laying of pipes is as follows: a trench is dug to a depth of circa 150 mm below the design bottom level of the pipe to allow for the placement of a layer of crushed stone pipe bedding material beneath the pipe. A steel protection box is placed in the trench to prevent the trench walls collapsing on the workers.
A crushed stone bedding material is then poured into the trench using an excavator or other means and the workers in the trench then manipulate this material to form the bedding layer for the pipe.
Great care must be taken to ensure that the top level of this bedding material is accurately aligned with the designed pipe gradient and the designed bottom level of the pipe and this is commonly achieved by measuring from an in pipe laser beam which is pre aligned to the pipe line and gradient.
The pipe is then lowered into the trench and the workers insert this pipe into a previously laid pipe and carefully adjust the pipe so as it is correctly aligned along the design line and gradient.
Additional crushed stone is then lowered into the trench and the workers place this stone either side and along the length of the pipe up to the halfway level on the pipe diameter.
This side fill stone is manipulated with a shovel or rod by inserting the tool into the gravel along both sides of the pipe thus ensuring that any voids that may exist within the stone are replaced with stone.
This is a key facet of the installation as the pipe relies on this stone to provide structural support to the pipe in the bedding and haunch zones, the bedding zone been the area underneath the pipe and the haunch zone being the area at either side of the pipe up to a level halfway up the circumference of the pipe to a level known as the springline. Improperly supported pipes may move or dislodge during and after infilling of the trench leading to additional excavation or realignment of pipes which adds considerable time and expense to the pipe laying process.
There remains a need for alternative devices capable of minimising human intervention in placing materials in a trench, thereby reducing the potential for injury resulting from trench collapse. Moreover, the device should be capable of setting a pipe secured therein to a specific slope or gradient and further provide for automated delivery and compaction of additional aggregate material such as crushed stone along either side and along the length of the pipe to ensure proper support of the laid pipe without requiring workers to operate in the trench in the manner described above.